Wear is well known for causing material loss in a sliding interface. Available macroscopic approaches are bound to empirical fitting parameters. We propose a study of the physical processes that lead to wear at the scale of the surface roughness, where adhesive junctions are formed between the asperities on the surface of the materials. Using a brittle formulation of the variational phase-field approach to fracture, we demonstrate that the failure mechanism of an adhesive junction can be linked to its geometry. By imposing specific couplings between the damage and the elastic energy, we further investigate the triggering processes underlying each failure mechanism. We show that a large debris formation is mostly triggered by tensile stresses while shear stresses are dominating the mechanisms leading to small or no particle formation. The interaction of two neighboring junctions is analyzed and shows that macro-particles which embody the two junctions can be formed under certain conditions. A ductile phase-field formulation permits us to assess the effect of the material’s ductility on the failure mechanism of adhesive junctions. We observe that the formation of large particle becomes less likely to happen as the ductility of the material increases.